1. Field of the Invention
This invention relates to a process for producing an electrophotographic photosensitive member.
2. Related Background Art
Electrophotographic photosensitive members are constituted basically of a photosensitive layer on which a latent image is formed by electrostatic charging and exposure to light and a substrate on which the photosensitive layer is provided.
Meanwhile, electrophotographic photosensitive members are required to have sensitivities, electric properties and optical characteristics in accordance with electrophotographic processes applied.
They are also required to have an environmental stability in any environment of from low temperature/low humidity to high temperature/high humidity which is high enough to well exhibit their performances.
Faulty images are exemplified typically by white lines, black spots in white background areas, white spots in black background areas, background fog in white background areas, and also interference fringes caused by factors such as surface shape of substrates and uneven layer thickness of photosensitive members in the case of apparatus such as digital copying machines and laser beam printers in which exposure is effected using a light source having a single wavelength. Accordingly, in the manufacture of photosensitive members, some countermeasures must be taken previously so that these faulty images do not occur.
As a factor having a great influence when such faulty images occur, there can be given the surface state of a substrate.
Substrates having not been treated at all after molding usually do not necessarily have any surface state as it is which is most suited for photosensitive members. Hence, problems caused by the surface state may occur in many instances.
To solve such problems, conventionally, as disclosed in, e.g., Japanese Patent Applications Laid-open No. 1-123246 and No. 64-86153, the photosensitive layer is formed after the surface of an aluminum substrate has been ground on a lathe. In particular, in the case of photosensitive members for digital systems, it is proposed to grind the surface of a substrate to have an appropriate unevenness so as to prevent interference fringes.
When, however, the aluminum substrate is ground, continuous work marks may remain in the peripheral direction. Hence, streaky faulty images may appear in halftone images, or, in particular, moires tend to occur because of the relationship between digital images and laser scanning lines.
Japanese Patent Applications Laid-open No. 7-43922 and No. 8-1510 disclose roller burnishing made on the periphery of a substrate. This method can provide a surface which is uneven without regularity. However, since a hard grindstone is rotated at a high speed to grind the substrate surface, abrasive grains having come off or grind dust may affect the substrate surface to tend to be deeply scratched in places, and scratches thus made may be left when photosensitive members are manufactured, to cause faulty images.
Japanese Patent Application Laid-open No. 6-35216, Japanese Patent No. 2668985, Japanese Patent Publication No. 7-15589 and Japanese Patent Application Laid-open No. 9-179322 also disclose a method in which the surface of an aluminum substrate is abraded by wet honing. This method is an effective way of providing a surface which is uneven without regularity. However, this can not prevent injection of electric charges from the substrate.
Meanwhile, methods have hitherto been proposed, as exemplified by a method in which the surface of an aluminum substrate is subjected to chromating to form a chromated chemical conversion coating, as disclosed in Japanese Patent Applications Laid-open No. 54-12733 and No. 57-62056; a method in which a boehmite coating is formed on the surface of an aluminum substrate, as disclosed in Japanese Patent Applications Laid-open No. 58-14841 and No. 64-29852; and a method in which the surface of an aluminum substrate is oxidized forcedly by high-temperature treatment to form an oxide film, as disclosed in Japanese Patent Applications Laid-open No. 57-29051.
With regard to, e.g., the method of chromating, substrates having a certain degree of performance can be obtained. However, since treating solutions contain chromium, it is very difficult to dispose of waste liquor, and also this is not preferable in view of environmental safety.
With regard to the boehmite treatment, the crystal state of the surface can not be said to be suited for substrates of electrophotographic photosensitive members. It can be effective to a certain degree with regard to electrophotographic performance, but, with regard to images, no satisfactory image quality has been achieved because the surface structure and shape are unsuited. Thus, under existing circumstances, those satisfying all performances have not been available.
What is aimed by the above surface treatment is that the film formed on the substrate surface prevents any non-uniformity from being caused in electrophotographic performances and images by electric charges injected locally from the substrate to the photosensitive layer.
As a method of preventing such local charge injection so as to cause no faulty images, a method is available in which the surface of an aluminum substrate is subjected to anodizing to provide a layer of aluminum oxide (e.g., Japanese Patent Applications Laid-open No. 2-7070 and No. 5-34964).
This method is a good method in order to attain such an aim. However, in order to form the layer uniformly without causing any uneven layer thickness on the substrate surface, it must be formed in a certain larger thickness, and a thickness of about 5 or 6 xcexcm or more under usual conditions for its formation. Hence, the layer must be formed in a much larger thickness than the thickness actually required as a charge injection blocking layer, resulting in an increase in cost.
Accordingly, an object of the present invention is to provide a process by which an electrophotographic photosensitive member having good electrophotographic performances that may cause no faulty images in any environment of from low temperature/low humidity to high temperature/high humidity and also may less cause potential variations can be produced at a low cost and stably.
As a result of studies made in order to solve the problems discussed above, the present inventors have discovered the following: It is a very effective means to form on the substrate an insoluble coating with specific composition by applying specific chemical conversion to the surface of an aluminum substrate used in the electrophotographic photosensitive member, i.e., by chemical reaction between the substrate and an aqueous acid solution containing a specific metal element, without use of any electrical external force. This is effective in view of the advantages that the cost and environment can be made very less adversely affected and the production apparatus can be made simpler than in the anodizing.
In addition, as a preliminary step of this chemical conversion, the aluminum substrate is etched with at least one of an acid and an alkali. This makes it possible to obtain a substrate for electrophotographic photosensitive members having superior performances.
The present invention provides a process for producing an electrophotographic photosensitive member, comprising at least one of the following steps a) and b) and the following steps c) and d) of;
a) etching an aluminum substrate with at least one of an acid and an alkali;
b) abrading an aluminum substrate with an abrasive dispersion containing 5% by volume or more of a spherical abrasive having a 50% diameter of from 5 xcexcm to 60 xcexcm as measured in cumulative percentage;
c) subjecting the aluminum substrate having been processed by at least one of the steps a) and b), to chemical conversion with an aqueous acid solution containing a salt of titanium or a salt of zirconium; and
d) forming a photosensitive layer on the aluminum substrate having been subjected to the chemical conversion.